题目

Sales of CDs have greatly increased since the early 1990s, when people _______ to enjoy the advantages of this new technology. A. begin B. began C. have begun D. had begun 答案：B 解析: 此题考查since以及定语从句的时态照应。since加过去时间点，主句自然用完成时态。既然since跟的是过去的时间点，那么when指代的当然就是过去时间in the early 1990s，所以选过去式began。

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